Controlling vehicle brakes

ABSTRACT

An apparatus for controlling braking of a vehicle having a plurality of brake-packs. The apparatus includes a controller configured to receive a first plurality of input values having a first scatter value; calculate an adjustment factor for each brake-pack based on the received first plurality of input values; output a control signal to cause each brake-pack of the plurality of brake-packs to be applied at a pressure based on the adjustment factor calculated for that brake-pack; and receive a second plurality of input values having a second scatter value. Each input value relates to a different one of the plurality of brake-packs. The adjustment factors are calculated such that the second scatter value is less than or equal to the first scatter value.

RELATED APPLICATION

This application claims priority to United Kingdom (GB) patentapplication no. 1709900.3, filed Jun. 21, 2017, the entire contents ofwhich is hereby incorporated by reference.

TECHNICAL FIELD

The present invention relates to an apparatus for controlling braking ofa vehicle having a plurality of brake-packs.

BACKGROUND

Regulations require aircraft brakes to be able to handle an abortedtakeoff at any moment prior to the plane leaving the runway. Brakesshould not exceed a specified temperature, to avoid performancedegradation. Current design prohibits an aircraft from taking off if itsbrakes are too hot (e.g. carbon temperature above 400° C., correspondingto an indicated temperature of about 300° C.). To ensure that the brakesare cool enough even after use during taxiing out to the runway, it isrecommended that an aircraft is not dispatched if its brakes are above apredefined temperature (e.g. 150° C., as measured by a brake temperaturesensor), which is significantly lower than the maximum permittedtake-off temperature and allows for temperature increase during taxibraking.

Application of the brakes of an aircraft can be instigated (demanded) bythe flight crew applying pressure to the brake pedals, or by anauto-brake function. When such a braking demand is made, the hydraulicpressure is increased in a number of braking pistons, which apply forceto press together the rotors and stators within the brake pack. Assumingthat the same braking demand is made of each landing gear (e.g. by theflight crew applying pressure to each brake pedal), the hydraulicpressure in each brake-pack of a landing gear is assumed to be equal.

However; applying equal hydraulic pressure to each brake-pack does notnecessarily result in optimal braking performance, or in an optimalturnaround time. Each brake-pack has a brake gain, which defines howmuch torque is developed per unit of pressure applied. This brake gaincan vary from brake-pack to brake-pack (e.g. due to manufacturingtolerances), meaning that each brake-pack may develop a different levelof braking torque for the same level of applied pressure.

Furthermore, each brake-pack may be in a different state of wear. Wherethis is the case, if the torque (and therefore the energy) developed byeach brake-pack is identical, each brake-pack will heat at a differentrate, with the heating rate being determined by the brake mass.Consequently, each brake-pack will reach a different peak temperature,and will take a different amount of time to cool down to a targettemperature suitable for pushback from the stand. If the torquedeveloped by each brake-pack is also different, due to variation inbrake gain as explained above, differences in peak temperature andcooling time between the brake-packs may be even more significant.

SUMMARY

A first aspect of the present invention provides an apparatus forcontrolling braking of a vehicle having a plurality of brake-packs. Theapparatus comprises a controller configured to receive a first pluralityof input values having a first scatter value; calculate an adjustmentfactor for each brake-pack based on the received first plurality ofinput values; output a control signal to cause each brake-pack of theplurality of brake-packs to be applied at a pressure based on theadjustment factor calculated for that brake-pack; and receive a secondplurality of input values having a second scatter value. Each inputvalue relates to a different one of the plurality of brake-packs. Theadjustment factors are calculated such that the second scatter value isless than or equal to the first scatter value.

Optionally, the controller is operable in a first mode in which eachinput value is a value of a first parameter, and in a second mode inwhich each input value is a value of a second, different, parameter.Optionally, the apparatus is configured to operate the controller ineither the first mode or the second mode based on a current state of thevehicle. Optionally, the apparatus is configured to operate thecontroller in the first mode if a predefined first mode criterion ismet, and to operate the controller in the second mode if a predefinedsecond mode criterion is met. Optionally, in the first mode each inputvalue is a torque value indicating an amount of torque reacted by adifferent one of the plurality of brake-packs. Optionally, in the secondmode each input value is a cooling time value indicating a predictedtime required for a different one of the plurality of brake-packs toreach a predetermined temperature.

Optionally, the predefined first mode criterion comprises a minimumground speed of the vehicle, and is defined such that it is met when aground speed of the vehicle is greater than the minimum ground speed.Optionally, the predefined second mode criterion comprises a maximumground speed of the vehicle, and is defined such that it is met when aground speed of the vehicle is less than the maximum ground speed.Optionally, the predefined second mode criterion comprises a minimumbrake temperature, and is defined such that it is met when thetemperatures of the brake-packs of the vehicle are all above the minimumbrake temperature.

Optionally, the controller is further operable in a third mode in whicheach input value is a value of a third parameter, and the apparatus isconfigured to operate the controller in the third mode if a predefinedthird mode criterion is met. Optionally, the third parameter isbrake-pack temperature, and the predefined third mode criterioncomprises a maximum ground speed of the vehicle and a minimum braketemperature, and is defined such that it is met when a ground speed ofthe vehicle is less than the maximum ground speed and the temperature ofat least one brake-pack is below the minimum brake temperature.Optionally, the predefined third mode criterion is defined such that itis met when a ground speed of the vehicle is less than the maximumground speed and the temperatures of all the brake-packs are below theminimum brake temperature.

Optionally, the apparatus is configured to receive vehicle stateinformation comprising one or more of: current ground speed of thevehicle; temperature of each brake-pack; current flight cycle phase.Optionally, the apparatus is configured to select an operating mode ofthe controller based on the received vehicle state information.

Optionally, the vehicle is an aircraft. Optionally, each brake-pack is acarbon brake-pack.

A second aspect of the present invention provides an aircraft comprisinga plurality of brake-packs; a plurality of torque sensors; a source ofbrake temperature information; a brake cooling prediction system; and anapparatus according to the first aspect. Each torque sensor isconfigured to measure the torque reacted by a different one of theplurality of brake-packs. The source of brake temperature information isfor generating a value of the temperature of each different one of theplurality of brake-packs. The brake cooling prediction system is forpredicting a time required by each brake-pack to reach a predeterminedtemperature. The apparatus is in communication with the plurality oftorque sensors, the source of brake temperature information, and thebrake cooling prediction system. The apparatus is configured to receivethe first plurality of input values and the second plurality of inputvalues from a selected source comprising one of: the plurality of torquesensors; the source of brake temperature information; and the brakecooling prediction system. The source is selected based on a currentstate of the aircraft.

Optionally, the aircraft further comprises a ground speed sensor incommunication with the apparatus, and the apparatus is configured toreceive ground speed information from the ground speed sensor.Optionally the apparatus is configured to select the source based on thereceived ground speed information.

Optionally, the apparatus is configured to receive brake temperatureinformation from the source of brake temperature information, and toselect the source based on the received brake temperature information.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of exampleonly, with reference to the accompanying drawings, in which:

FIG. 1 shows a schematic view of an apparatus for controlling braking ofa vehicle according to an example;

FIG. 2 shows an example plot of brake temperature against time for twodifferent brake-packs of a vehicle;

FIG. 3 shows a schematic view of an example controller for the apparatusof FIG. 1; and

FIG. 4 is a schematic view of an example aircraft comprising anapparatus according to an example.

DETAILED DESCRIPTION

The examples described herein relate to a Brake Temperature & TorqueControl (BTTC) apparatus, for controlling the operation of a vehicle'sbrakes. The described examples relate to aircraft, and it is envisagedthat the invention will have particular advantages when used on anaircraft, but it may also be beneficially implemented on other types ofvehicle.

Braking performance can be improved by ensuring that equal torque isdeveloped by each brake-pack during a brake application, because thisensures that each brake-pack provides the same stopping power. Where thevehicle is an aircraft, or any other vehicle for which an operationalcycle typically includes a brake cooling period, turnaround time (TAT)can be improved by ensuring that the torque developed from eachbrake-pack results in a brake-pack temperature for which the time tocool to a target temperature is the same as for every other brake-packon the vehicle.

FIG. 2 shows an example plot 21 a of a time-series of values of thetemperature of a first brake-pack of an aircraft and an example plot 21b of a time-series of values of the temperature of a second brake of theaircraft. Each plot covers a first period during which main landingbraking (represented by the peaks 22 a, 22 b) occurred, a second periodduring which the brake-packs were cooling following main landing braking(including minor peaks 23 a, 23 b representing a braking snub duringtaxi-in), and a third period during which the brake-packs were atambient temperature (so no further cooling occurred), until a furtherbraking snub (represented by the peaks 24 a, 24 b) occurred duringtaxi-out. In this example, the braking pressure is evenly distributedbetween the first and second brake-packs. The first and secondbrake-packs are on the same axle and therefore they exhibit similarthermal behaviour. However; it can be seen that the first brake-packreaches a higher peak temperature as a result of each brakingapplication. This could be, for example, because the first brake-pack ismore worn and therefore has less mass than the second brake-pack. Theheating and cooling rates are also slightly different between the twobrake-packs. As a result of these differences, the first brake-packreaches ambient temperature at a later time than the second brake-pack.

The example BTTC apparatus seek to achieve the advantages of improvedbraking performance and reduced TAT by distributing braking pressurebetween the braked wheels in a selected manner, to achieve a selectedoutcome. Where the vehicle is an aircraft, the selected outcome (andtherefore the selected manner in which the BTTC apparatus distributesthe brake pressure) may vary in dependence on the flight cycle phase. Inparticular, the example BTTC apparatus may seek to control the scatterof brake torques, brake temperatures or cooling times between differentbrake-packs of a vehicle (because of differences in brake gain and brakemass) without altering a total amount of braking provided by the brakes.

It will be appreciated that scatter of brake torques, brake temperaturesand brake cooling times cannot be simultaneously controlled. Therelative impact of variances in these different parameters differsdepending on the operational situation of the vehicle. For an aircraft,the relative impact of variances in brake torques, temperatures andcooling times will differ depending on flight cycle phase. As such, someof the example BTTC apparatus seek to achieve optimum brakingperformance and TAT can be achieved by controlling different parametersduring different flight cycle phases.

FIG. 1 shows an example BTTC apparatus 1. The BTTC apparatus 1 can beused to control braking of a vehicle having a plurality of brake-packs,and in particular to control braking of an aircraft during landing andtaxiing. In the following description, the term “brake application” isused to refer to any operation of the vehicle's brakes during which acertain level of braking pressure is applied by each brake-pack (e.g. topress together brake discs of the brake-pack) to achieve an overallbraking pressure corresponding to a “demanded braking pressure” demandedby an operator of a vehicle (which may be a human operator or anautomatic system). A brake application causes energy to be input to thebrake-packs and therefore the temperature of the brake-packs toincrease. A brake application is typically performed for the purpose ofslowing the vehicle.

The BTTC apparatus 1 comprises a controller 10, which is connected by acommunications link 11 to at least one source of input data and is alsoconnected by a communications link 12 to a braking controller of avehicle on which the BTTC apparatus is installed. The source of inputdata (which does not form part of the present invention) may be anysystem or mechanism able to provide a data signal to the controller 10,such as an aircraft avionics system, a monitoring system, a sensor, orthe like. The braking controller (which does not form part of thepresent invention) may be any system or mechanism which is able to causethe brakes of the vehicle to be applied in response to an input signal.In particular, the braking controller is able to cause each brake-packof the vehicle to apply a particular pressure specified by an inputsignal, which may be different for different brake-packs. In someexamples the braking controller is an aircraft braking control system.Each of the communications links 11, 12 may be wired, wireless, or partwired and part wireless. In some examples the BTTC apparatus 1 iscomprised in an aircraft braking control system. At least somecomponents of the BTTC apparatus 1 can be configured to receive powervia a connection to an aircraft avionics system.

The controller 10 is configured to receive a first plurality of inputvalues having a first scatter value, wherein each input value relates toa different one of the plurality of brake-packs, via the communicationslink 11. Each input value of the plurality of input values is of thesame type (that is, the input values are values of the same parameter).The number of input values comprised in the plurality of input valuesmay be the same as the number of brakes of the vehicle. For example, foran aircraft having four brake-packs, the first plurality of input valueswill comprise four input values (one for each brake-pack). In principle,the input values may be values of any parameter relating to abrake-pack. Such parameters include (but are not limited to) brake-packtemperature, braking torque, and predicted brake-pack cooling time (thatis, time for the brake-pack to cool from a current temperature to apredetermined target temperature). The input values may be measuredvalues measured by a sensor of the vehicle. The input values may becalculated values calculated based on measured values. The input valuesmay be current values, meaning that each input value represents the mostrecently measured state of the brake-pack with which that value isassociated. In some examples the controller 10 is configured tocontinuously receive input values during a time period when the BTTCapparatus is operational. In some examples the controller 10 isconfigured to continuously or periodically receive current input valuesduring a brake application. In some examples the controller 10 may beconfigured to receive input values in real or near-real time. Each inputvalue may be comprised in a time-varying signal, which is continuouslyreceived by the controller 10 during operation of the BTTC apparatus.

The controller 10 is further configured to calculate an adjustmentfactor for each brake-pack based on the received first plurality ofinput values. The purpose of the adjustment factor is to redistributebraking pressure (or braking torque) between the plurality ofbrake-packs to achieve or promote a selected outcome. A conventionalaircraft (that is, one not equipped with a BTTC apparatus according tothe invention) will typically cause each brake-pack to be applied withequal pressure to achieve an overall brake pressure corresponding to ademanded amount of braking. As explained above, there are variousscenarios in which it may be advantageous to vary the pressure (ortorque) distribution between the brake-packs. The controller 10 achievesthis by calculating different adjustment factors for each brake-pack,which adjust the amount of pressure applied by each brake-pack to belarger or smaller (or possibly the same) as the default equal pressureamount. In some examples the controller 10 may calculate a pressureadjustment factor for adjusting a default pressure amount, in otherexamples the controller 10 may calculate a torque adjustment factor foradjusting a torque corresponding to a default pressure amount. In suchexamples a torque feedback loop may be used to control the pressureapplied by each brake during a braking application, so as to achieve theadjusted torque values.

The adjustment factors are calculated such that the scatter value of asubsequently received plurality of input values is less than or equal tothe first scatter value. That is, the adjustment factors alter thedistribution of braking pressure between the brake-packs in a manner soas to equalize (as far as possible) contemporaneous input values of thebrake-packs. The adjustment factors are also calculated such that theoverall brake pressure (or brake torque) is not altered. So, forexample, if the pressure to be applied by one brake-pack is reduced byits adjustment factor, the pressure to be applied by at least one of theother brake-packs must be increased. An adjustment factor may, forexample, be in the form of a coefficient which is multiplied togetherwith a default equal brake pressure (or a default equal brake torque) togenerate an adjusted brake pressure (or torque). In such examples thesum of the coefficients for all of the brake-packs may be 1. Thecontroller 10 may be configured to continuously or periodicallycalculate updated adjustment factors, as new input values are received.

The controller 10 is further configured to output a control signal, viathe communications link 12, to cause each brake-pack of the plurality ofbrake-packs to be applied at a pressure based on the adjustment factorcalculated for that brake-pack. The control signal is output to thebraking controller of the vehicle, either directly or via anothervehicle system (such as an avionics system). The control signal may beof any suitable form which is receivable by the braking controller andusable by the braking controller to implement a braking application. Thecontrol signal may comprise a plurality of pressure values, eachassociated with a different brake-pack of the vehicle. The controlsignal may comprise a plurality of torque values, each associated with adifferent brake-pack of the vehicle. The plurality of pressure values(or torque values) may be adjusted pressure (or torque) valuescalculated using the adjustment factors. The control signal may beoutput continuously, or periodically, during a brake application.Information contained in the control signal may be updated over thecourse of a braking application. For example, an updated control signalmay be output for each set of updated adjustment factors calculated bythe controller 10.

The controller 10 is further configured to receive a second plurality ofinput values having a second scatter value. The second plurality ofinput values are of the same type as the first plurality of input values(that is, they are values of the same parameter). The second pluralityof input values is received in the same manner as the first plurality ofinput values. In some examples the second plurality of input values arecomprised in the same time varying signals as the first plurality ofinput values. The second plurality of input values is received at alater time than the first plurality of input values (it is assumed thatthe controller has not switched to a different operational mode betweenthe first time and the later time). The second plurality of input valuesis received after the control signal has been output, and thereforeafter the brake-packs of the vehicle have been applied according to thecalculated pressure adjustment values. A scatter value of the secondplurality of input values should therefore be less than or equal to thefirst scatter value.

FIG. 3 shows the layout of a particular example controller 30 suitablefor use as the controller 10 of the apparatus 1. The example controller30 is configured for use on a vehicle having four braked wheels, andreceives a time-varying input signal in respect of each braked wheel.Although single lines are shown in FIG. 2, the original input is avector of four signals, and this is true throughout the controller,apart from where the four signals are summed into a single value.

The example controller 30 works on the assumption that eachcontemporaneous set of four input values (one for each of the fourbraked wheels) should be the same, each being 25% of the sum of the fourinput values. When this is not the case, regardless of what the inputparameter may be, the controller 30 calculates the percentagecontribution to the total sum from each input value, and hence finds thedeviation from the required 25% contribution (part A). By integratingeach input signal with respect to time, the controller calculates anadjustment factor for each input value. The adjustment factors comprisea set of four coefficients (one for each input value), which can beapplied to a pressure demand signal to redistribute braking pressurebetween the braked wheels in a manner so as to reduce each deviation to0 (part B). Once a coefficient has been calculated for each of the fourinput values, the four coefficients are normalized, ensuring that thesum of the four coefficients is equal to 1. This ensures that theoverall braking pressure applied will not change from that which wasdemanded, even though the distribution may have changed.

In the particular illustrated controller, part A calculates the errorbetween the demanded contribution and the actual contribution, part Bapplies a proportional integral derivative (PID) controller, and part Censures that the sum is equal to 1. It will be appreciated that theparameters may vary from what is shown in FIG. 3, and certain terms maybe omitted. The settings used for the integral control may varyaccording to which parameter is being controlled (i.e. which parameterthe input values are values of). Generally, it is expected that thesettings will be determined on a case by case basis, e.g. throughexperimentation to find settings which minimise response time withoutcompromising performance.

It may be advantageous to control different parameters during differentscenarios. For an aircraft, for example, it may be advantageous tocontrol different parameters during different phases of a flight cycle.As such, in some examples the controller 10 is operable in a first modein which each input value is a value of a first parameter, and in asecond mode in which each input value is a value of a second, different,parameter. In such examples the BTTC apparatus 1 is configured tooperate the controller 10 in either the first mode or the second mode independence on a current state of the vehicle. The controller 10 mayfurther be operable in a third mode in which each input value is a valueof a third parameter, different to the first and second parameters. Insuch examples the BTTC apparatus 1 may be configured to operate thecontroller 10 in either the first mode, the second mode or the thirdmode in dependence on a current state of the vehicle.

Three possible operational modes suitable for an aircraft application ofthe BTTC apparatus 1 will now be described. In the described example,the first mode controls the distribution of braking torques between thebrake-packs, the second mode controls the distribution of predictedbrake-pack cooling times, and the third mode controls the distributionof brake-pack temperatures.

Mode 1—Torque Control

During main landing braking of an aircraft (at speeds above a certainthreshold, which may for example be about 30 knots) it is desirable tocontrol the braking torque so that the torque exerted by each brake isequal, because equal torques result in a more consistent brakingperformance. As such, the BTTC apparatus 1 is configured to operate thecontroller 10 in the first (torque control) mode during the main landingbraking phase of a flight cycle (that is, the main braking phase of alanding). If the brake gain differs between the brake-packs of theaircraft (as will almost certainly be the case in practice), eachbrake-pack will require a different amount of braking pressure toachieve the same overall torque. The controller 10 determines brakingpressures suitable to achieve an equal torque distribution whenoperating in the first mode.

In the first mode each input value to the controller 10 comprises atorque value indicating an amount of torque reacted by a different oneof the plurality of brake-packs. In the particular example, the inputvalues are measured braking torque values (e.g. measured by torquesensors on the aircraft wheels). The controller 10 is configured toequalize these measured torque values by calculating coefficients foradjusting the demanded braking pressures, in the manner described abovein relation to FIG. 2. The controller 10 forms part of a feedback loop,and thereby continually updates the coefficients during the time periodin which it is operating in the first mode, to achieve or maintain anequal torque distribution between all of the brake-packs. Therelationship between braking pressure and braking torque is simple anddirect, meaning that once an equal distribution has been achieved,further significant changes to the coefficients are unlikely to berequired in order to maintain the equal distribution.

Operating the controller 10 in the first (torque control) mode canadvantageously improve braking performance, for the reasons describedabove. However; it may not necessarily improve the aircraft turnaroundtime because the first mode does not take brake temperature or predictedbrake cooling time into account. As such, the BTTC apparatus 1 may beconfigured to operate the controller in the first mode only undercertain circumstances (e.g. when maximising braking performance is ofparticular importance, such as during the main braking phase of alanding). In some examples the BTTC apparatus 1 may be configured tooperate the controller 10 in the first mode and not in any of the othermodes, for as long as certain predetermined conditions for operating inthe first mode are met.

In some examples the BTTC apparatus 1 comprises at least one predefinedfirst mode criterion, and is configured to operate in the first mode ifthe at least one predefined first mode criterion is met. For example,the at least one predefined first mode criterion may comprise a minimumground speed and be defined such that it is met when a measured groundspeed is greater than the minimum ground speed. In some examples theminimum ground speed is equal to a threshold speed for differentiating amain landing phase from a taxi-in phase. In some examples the minimumground speed is 30 knots, such that the at least one predefined firstmode criterion is only met during the main braking phase of a landing.The minimum ground speed may be at least 30 knots. The at least onepredefined first mode criterion may be part of software control logic ofthe BTTC apparatus 1, or may be stored in a memory comprised in oraccessible to the BTTC apparatus 1.

Mode 2—Cooling Time Control

During taxiing immediately after landing the aircraft ground speed issignificantly less than during main landing braking (generally less than30 knots), meaning that optimal brake performance is less important.During this phase of the flight cycle the brake-pack temperatures aregenerally above the temperature required for pushback, so it isdesirable to cool the brake-packs as quickly as possible in order toachieve an optimal aircraft turnaround time. The second (cooling timecontrol) mode is configured to reduce or minimize the total cooling time(that is, the time required for all brake-packs to reach an acceptablepushback temperature) by distributing the braking energy between all ofthe brake-packs so as to harmonize predicted cooling times (to apredefined target temperature) of the brake-packs. The predefined targettemperature may be a pushback temperature.

The peak temperature reached by a brake-pack during a brakingapplication is dependent on the amount of energy put into the brake-packduring that braking application (which will vary with brake gain) andthe mass of the brake-pack. The time required for a brake-pack to cooldown is dependent on the current temperature of the brake-pack and themass of the brake-pack (along with other factors which will be common toall the brake-packs, such as ambient temperature). A predicted coolingtime can be calculated for each brake by determining the peaktemperature reached by that brake-pack, and then determining a time forthat brake to cool from the peak temperature to the predefined targettemperature.

The predicted cooling times can be calculated by the controller 10.Alternatively, the predicted cooling times can be calculated by aseparate brake cooling time prediction system configured to providecooling time prediction information to the controller 10. Any suitabletechnique may be used to calculate predicted brake-pack cooling times.An example of a suitable system and process for calculating a predictedcooling time of a brake is described in European patent application no.17168146.3.

In the second (cooling time control) mode each input signal to thecontroller comprises a cooling time value indicating a predicted timerequired for a different one of the plurality of brake-packs to reach apredetermined temperature. The cooling time values may change during thetime period in which the controller 10 is operating in the second mode,due to changes in ambient conditions, further brake applications, and soon, which occur during this time period. The controller 10 continuallyor periodically receives updated cooling time values for each brake-packduring the time period in which it is operating in the second mode. Whenoperating in the second mode, the controller 10 is configured tocalculate coefficients for adjusting the demanded braking pressures soas to equalize (or at least minimize the deviation in) the predictedcooling times, in the manner described above in relation to FIG. 2. Thecontroller may continually or periodically update the calculatedcoefficients during the period in which it is operating in the secondmode, based on the most recently received predicted cooling time data.

Unlike the relationship between braking torque and braking pressure, therelationship between braking pressure and brake-pack cooling time is notsimple (partly due to the influence of external factors on coolingtimes—such external factors may include one or more of ambienttemperature, direct sunlight, wind speed and direction, and the like).Consequently, it is likely that the calculated coefficients will varysignificantly during a given time period in which the controller 10 isoperating in the second mode (which may, e.g., correspond to part or allof a taxiing-in flight cycle phase).

Reducing the scatter between brake-pack cooling time values is aneffective way of reducing aircraft turn-around times. Therefore, it maygenerally be desirable for the controller 10 to operate in the secondmode whenever braking performance is not critical. In some examples theBTTC apparatus 1 is configured to operate the controller 10 in thesecond mode whenever the conditions for operating the controller in thefirst mode are not met. In some examples the BTTC is configured tooperate the controller in the second mode whenever the conditions foroperating the controller in the first mode are not met and conditionsfor operating the controller in the third mode are not met.

In some examples the BTTC apparatus comprises at least one predefinedsecond mode criterion, and is configured to operate in the second modeif the at least one predefined second mode criterion is met. Forexample, the at least one predefined second mode criterion may comprisea maximum ground speed and may be defined such that it is met when ameasured ground speed is less than (or is less than or equal to) themaximum ground speed. In some examples the maximum ground speed is equalto a threshold speed for differentiating a main landing phase from ataxi-in phase. In some examples the maximum ground speed is 30 knots.The maximum ground speed may be at least 30 knots. The maximum groundspeed may be the same as a minimum ground speed comprised in apredefined first mode criterion. In some examples the at least onepredefined second mode criterion is defined such that it is only metwhen the at least one predefined first mode criterion is not met. Insome examples the at least one predefined second mode criterion maycomprise a requirement that the at least one predefined first modecriterion is not met, and/or a requirement that at least one predefinedthird mode criterion (e.g. as described below) is not met. In someexamples the at least one predefined second mode criterion is definedsuch that it is only met if all brake-pack temperatures are above thepredefined target temperature. The at least one predefined second modecriterion may be defined such that it is only met during a taxi-in phaseof a flight cycle. The at least one predefined second mode criterion maybe part of software control logic of the BTTC apparatus 1, or may bestored in a memory comprised in or accessible to the BTTC apparatus 1.

Third Mode—Temperature Control

In the third (temperature control) mode each input signal to thecontroller comprises a brake-pack temperature value indicating thetemperature of a different one of the plurality of brake-packs. Thebrake-pack temperature values may be measured values, e.g. measured bybrake temperature sensors of the aircraft. Alternatively the brake-packtemperature values may be calculated values, e.g. calculated by a braketemperature calculating function. Such a function may be comprised inthe BTTC 1, in a brake cooling time prediction system, or in any othersystem of the aircraft. Brake-pack temperature values may be calculated,for example, based on a measured braking torque for a given brake and aknown mass of the given brake.

The brake-pack temperature values may change during the time period inwhich the controller 10 is operating in the third mode, due to changesin ambient conditions, further brake applications, and so on, whichoccur during this time period. The controller 10 continually orperiodically receives updated temperature values for each brake-packduring the time period in which it is operating in the third mode. Whenoperating in the third mode, the controller 10 is configured tocalculate coefficients for adjusting the demanded braking pressures soas to equalize (or at least minimize the deviation in) the brake-packtemperatures, in the manner described above in relation to FIG. 2. Thecontroller 10 may continually or periodically update the calculatedcoefficients during the period in which it is operating in the thirdmode, based on the most recently received brake-pack temperature values.

Reducing the scatter of peak brake-pack temperatures does not generallyresult in reduced turnaround times, and so it is not generallyadvantageous to control the brake-pack temperature distribution duringthe taxi-in phase, assuming that the brake-packs are hot enough torequire a significant cooling period. However; if at least one of thebrake-packs is below the target temperature during a period when theconditions for operating the controller in the first mode are not met(that is, during a taxiing phase when the ground speed is relativelylow), it may be desirable to operate the controller 10 in a third(temperature control) mode. In the third mode the controller 10 isconfigured to equalize (as far as possible) the distribution of peakbrake-pack temperatures. If one or more of the brake-packs is below thetarget temperature used to calculate cooling time values it will have acooling time value of 0, meaning that the second mode will not operateeffectively.

It could occur that one or more of the brake-packs drops below (or neverexceeds in the first place) the target temperature (that is, thepredefined target temperature used to calculate the cooling time values)during the taxi-in phase. If all of the brake-packs are below the targettemperature during the taxi-in phase, it may be advantageous to operatethe controller 10 in the third mode rather than in the second mode. Itis also advantageous to use the third mode during the taxi-out phase,because it can minimize the risk of one or more of the brake-packsbecoming unacceptably hot during taxi-out.

During the taxi-out phase short brake applications (taxi snubs) areexpected to occur. These snubs may cause the temperature of one or moreof the brake-packs to rise above the predefined target temperature usedto calculate the cooling time values. This is acceptable as long as noneof the brake-pack temperatures rise high enough to force a ‘Brakes Hot’warning, which occurs when a certain predefined threshold temperature(higher than the target cooling temperature) is reached). A different,higher, target temperature value may therefore be defined in respect ofthe third mode, as will be explained below. The likelihood of the‘Brakes Hot’ threshold being reached can be minimized by distributingthe braking pressure between the brake-packs in a manner such that thetemperature distribution of the brake-packs is equalized (as far aspossible).

In some examples the BTTC apparatus 1 is configured to operate thecontroller 10 in the third mode whenever certain conditions are met. Insome examples the BTTC apparatus 1 is configured to operate thecontroller 10 in the third mode whenever the conditions for operatingthe controller 10 in the first mode are not met and the conditions foroperating the controller 10 in the second mode are not met.

In some examples the BTTC apparatus 1 comprises at least one predefinedthird mode criterion, and is configured to operate the controller 10 inthe third mode if the at least one predefined third mode criterion ismet. For example, the at least one predefined third mode criterion maycomprise a maximum ground speed and may be defined such that it is metwhen a measured ground speed is less than (or is less than or equal to)the maximum ground speed. In some examples the maximum ground speed is30 knots. The maximum ground speed may be the same as a minimum groundspeed comprised in a predefined first mode criterion. The maximum groundspeed may be the same as a maximum ground speed comprised in apredefined second mode criterion. In some examples the at least onepredefined third mode criterion is defined such that it is only met whenthe at least one predefined first mode criterion is not met. In someexamples the at least one predefined second mode criterion may comprisea requirement that the at least one predefined first mode criterion isnot met, and/or a requirement that at least one predefined second modecriterion is not met. In some examples the at least one predefined thirdmode criterion is defined such that it is only met if at least onebrake-pack temperature is below a predefined threshold temperature. Insome examples the at least one predefined third mode criterion may bedefined such that it is only met during a taxi-out phase of a flightcycle. The at least one predefined third mode criterion may be part ofsoftware control logic of the BTTC apparatus 1, or may be stored in amemory comprised in or accessible to the BTTC apparatus 1.

A different predefined threshold temperature may be defined fordifferent scenarios and/or different aircraft states. For example, adifferent predefined threshold temperature may be defined for differentflight cycle phases. In particular, during landing and taxi-in thepredefined threshold temperature may be the target temperature used tocalculate cooling time values (which may correspond to a maximumpush-back temperature), whereas during taxi-out the predefined thresholdtemperature may be a maximum takeoff temperature. Using differentthreshold temperatures in this particular manner ensures that the thirdmode is used for the whole of the taxi-out phase (which is advantageousbecause brake-pack temperature equalization is most desirable duringthis phase), and that the second mode is used as much as possible duringtaxi-in (which is advantageous because brake-pack cooling timeequalization is most desirable during this phase).

The example BTTC apparatus 10 described above selects a mode ofoperation for the controller 10 based on vehicle state information.Where the vehicle is an aircraft, such vehicle state information may beindicative of a current flight cycle phase of the aircraft. The vehiclestate information may comprise measurement data generated by sensors ofthe vehicle, such as current ground speed, or current brake-packtemperature. However; alternative examples are envisaged in which thevehicle state information is received from an avionics or cockpit systemof an aircraft. For example, an avionics system may provide anindication of the current flight cycle phase of the aircraft to the BTTCapparatus 1. An avionics system may determine a current flight cyclephase of the aircraft in any suitable manner, including by receiving amanual input from flight crew. Further examples are envisaged in whichthe controller 10 may be manually switched from one mode to another bythe flight crew, in which cases the BTTC apparatus 1 is configured toreceive a control signal from a cockpit system indicating a desiredoperational mode.

FIG. 4 shows an aircraft 400 on which a BTTC apparatus according to theexamples (e.g. the BTTC apparatus 1) is installed. The aircraftcomprises a fuselage 401, wings 402, and main and nose landing gear 404.Two wheels 403 are attached to each landing gear 404. Each wheel 403 hasan associated brake-pack (not visible) for braking that wheel. Thebrake-packs may be carbon brake-packs. The aircraft 400 furthercomprises a brake cooling prediction system for predicting a timerequired by each brake-pack to reach a predetermined temperature. Thebrake cooling prediction system is configured to provide cooling timevalues for each brake-pack to the BTTC apparatus. The brake coolingsystem may be in communication with sensors of the aircraft 400 toobtain measurement data for use in generating cooling time values.

Each brake-pack has an associated sensor apparatus, in particular atorque sensor configured to measure the torque reacted by thatbrake-pack. The sensor apparatus associated with a given brake-pack mayalso comprise any other sensor for measuring a parameter relating to thebrake-pack or its associated wheel, such as a brake temperature sensor,a wheel speed sensor, a tyre pressure sensor, an environmental sensor orthe like. At least the torque sensors are configured to provide measuredvalues for each brake-pack to the BTTC apparatus. The torque sensors mayalso be configured to provide measured torque values for each brake-packto a brake temperature calculating function. Temperature values for eachbrake-pack may then be calculated by the brake temperature calculatingfunction, based on the measured torque values and known brake masses,and the calculated temperature values provided to the BTTC.Alternatively, in examples where each sensor apparatus comprises a braketemperatures sensor, the plurality of brake temperature sensors may beconfigured to provide measured temperature values for each brake-pack tothe BTTC. Some or all of the sensors of the brake-pack sensor apparatusmay be in communication with the brake cooling prediction apparatus.

The BTTC apparatus is configured to receive the first plurality of inputvalues and the second plurality of input values from a selected source.The selected source is one or more of: the torque sensors, temperaturesensors, a brake temperature calculating function; the brake coolingprediction system. The source is selected based on a current state ofthe aircraft, e.g. in the manner described above in relation to theoperation of the BTTC apparatus 1. The aircraft 400 further comprises aground speed sensor. In some examples the ground speed sensor is incommunication with the BTTC apparatus and the BTTC apparatus isconfigured to receive ground speed information from the ground speedsensor. In such examples the BTTC apparatus may select the source basedon received ground speed information. In some examples the BTTC isconfigured to receive brake temperature information (e.g. from a braketemperature calculating function or from a plurality of braketemperature sensors) and to select the source based on the receivedbrake temperature information.

The aircraft 400 further comprises a braking control system (not shown),and in some examples the BTTC apparatus is configured to output thecontrol signal to the braking control system to cause each of thebrake-packs to be applied at the pressure.

The aircraft 400 further comprises an avionics system 405, and in theparticular example the BTTC apparatus, the brake cooling predictionsystem and the braking control system are all comprised in the avionicssystem 405. The avionics system 405 is located in an avionics bay orcompartment. In the particular example the avionics bay is in the noseof the aircraft below the cockpit, but it may be in a different locationdepending on the type of aircraft.

The above embodiments are to be understood as illustrative examples ofthe invention. It is to be understood that any feature described inrelation to any one embodiment may be used alone, or in combination withother features described, and may also be used in combination with oneor more features of any other of the embodiments, or any combination ofany other of the embodiments. Furthermore, equivalents and modificationsnot described above may also be employed without departing from thescope of the invention, which is defined in the accompanying claims.

Where the term “or” has been used in the preceding description, thisterm should be understood to mean “and/or”, except where explicitlystated otherwise.

The invention claimed is:
 1. An apparatus for controlling braking of avehicle having a plurality of brake-packs, the apparatus comprising acontroller configured to: receive a first plurality of input valueshaving a first scatter value, wherein each input value of the firstplurality of input valves relates to a different one of the plurality ofbrake-packs; calculate an adjustment factor for each brake-pack of theplurality of brake packs based on the received first plurality of inputvalues; output a control signal to cause each of the brake-packs of theplurality of brake-packs to be applied at a pressure based on theadjustment factor calculated for that brake-pack; and receive a secondplurality of input values after each of the plurality of brake-packsapply pressure in response to the output control signal, wherein thesecond plurality of input values have a second scatter value; whereinthe adjustment factors are calculated such that the second scatter valueis less than or equal to the first scatter value, wherein the controlleris operable in a first mode in which each of the plurality of inputvalues is a value of a first parameter of the plurality of brake packs,and in a second mode in which each of the plurality of input values is avalue of a second parameter of the plurality of brake packs differentfrom the first parameter, wherein the apparatus is configured to operatethe controller in the first mode if a predefined first mode criterion ismet, and to operate the controller in the second mode if a predefinedsecond mode criterion is met, and wherein the predefined first modecriterion comprises a minimum ground speed of the vehicle, and thepredefined first mode criterion is met when a ground speed of thevehicle is greater than the minimum ground speed.
 2. The apparatusaccording to claim 1, wherein in the first mode each input value of thefirst parameter is a torque value indicating an amount of torque reactedby a different one of the plurality of brake-packs, and in the secondmode each input value of the second parameter is a cooling time valueindicating a predicted time required for a different one of theplurality of brake-packs to reach a predetermined temperature.
 3. Theapparatus according to claim 1, wherein the predefined second modecriterion comprises a maximum ground speed of the vehicle, and isdefined such that the second mode criterion is met when a ground speedof the vehicle is less than the maximum ground speed.
 4. The apparatusaccording to claim 1, wherein the predefined second mode criterioncomprises a minimum brake temperature, and is defined such that it ismet when the temperatures of the brake-packs of the vehicle are allabove the minimum brake temperature.
 5. The apparatus according to claim1, wherein the apparatus is configured to receive vehicle stateinformation comprising one or more of: current ground speed of thevehicle; temperature of each brake-pack; current flight cycle phase; andthe apparatus is configured to select an operating mode of thecontroller based on the received vehicle state information.
 6. Anapparatus according to claim 1, wherein the vehicle is an aircraft. 7.The apparatus according to claim 1, wherein each brake-pack is a carbonbrake-pack.
 8. The apparatus according to claim 1, wherein the firstparameter and the second parameters are each one of brake torque appliedto each of the plurality of brake packs, brake temperature of each ofthe plurality of brake pacts, and brake cooling time of each of theplurality of brake packs.
 9. An apparatus for controlling braking of avehicle having a plurality of brake-packs, the apparatus comprising acontroller configured to: receive a first plurality of input valueshaving a first scatter value, wherein each input value of the firstplurality of input valves relates to a different one of the plurality ofbrake-packs; calculate an adjustment factor for each brake-pack of theplurality of brake packs based on the received first plurality of inputvalues and the adjustment factor is calculated to reduce the firstscatter value; output a control signal to cause each of the brake-packsof the plurality of brake-packs to apply a braking pressure based on theadjustment factor calculated for the brake-pack; and receive a secondplurality of input values having a second scatter value, wherein eachinput value of the second plurality of input valves relates to adifferent one of the plurality of brake-packs and the second scattervalue is smaller than the first scatter value; wherein the controller isoperable in a first mode in which each of the input values is a value ofa first parameter, and in a second mode in which each of the inputvalues is a value of a second parameter different from the firstparameter; wherein the apparatus is configured to operate the controllerin either the first mode or the second mode based on a current state ofthe vehicle; wherein the controller is further operable in a third modein which each of the input values is a value of a third parameter,different than the first and second parameters, and wherein theapparatus is configured to operate the controller in the third mode if apredefined third mode criterion is met.
 10. The apparatus according toclaim 9, wherein the third parameter is brake-pack temperature, andwherein the predefined third mode criterion comprises a maximum groundspeed of the vehicle and a minimum brake temperature, and is definedsuch that the predefined third mode criterion is met when a ground speedof the vehicle is less than the maximum ground speed and the temperatureof at least one brake-pack is below the minimum brake temperature. 11.An aircraft comprising: a plurality of brake-packs; a plurality oftorque sensors, wherein each torque sensor being configured to measure atorque reacted by a different one of the plurality of brake-packs; asource of brake temperature information, wherein the brake temperatureinformation is for generating a value of the temperature of eachdifferent one of the plurality of brake-packs; a brake coolingprediction system for predicting a time required by each brake-pack ofthe plurality of brake packs to reach a predetermined temperature; andthe apparatus according to claim 1 and in communication with theplurality of torque sensors, the source of brake temperatureinformation, and the brake cooling prediction system; wherein theapparatus is configured to receive the first plurality of input valuesand the second plurality of input values from a selected sourcecomprising one of: the plurality of torque sensors; the source of braketemperature information; and the brake cooling prediction system,wherein the source is selected based on a current state of the aircraft.12. The aircraft according to claim 11, further comprising a groundspeed sensor in communication with the apparatus, wherein the apparatusis configured to receive ground speed information from the ground speedsensor and to select the ground speed sensor as the selected sourcebased on the received ground speed information.
 13. The aircraftaccording to claim 11, wherein the apparatus is configured to receivethe brake temperature information from the source of brake temperatureinformation and to select the source of brake temperature informationbased on the received brake temperature information.
 14. A method ofbraking an aircraft having a braking system with brake packs configuredto apply braking forces to wheels of the aircraft, the method including:operating a controller of the braking system in a first mode if a groundspeed of the aircraft exceeds a predefined minimum ground speed andoperating the controller in a second mode if the ground speed of theaircraft is slower than the predefined minimum ground speed; receivingby a controller a first group of input values, wherein the input valuesrepresent brake torque or brake pressure while the controller operatesin the first mode and the input values represent brake cooling timewhile the controller operates in the second mode; while the controlleroperates in the first and second modes, calculating a scatter valuebased on the first group of input valves; calculating by the controller,while operating in the first and second modes, an adjustment factor foreach of the brake packs based on the received first group of inputvalues, wherein the adjustment factor is calculated to reduce thescatter value; outputting by the controller, while operating in thefirst and second modes, a control signal to cause each of the brakepacks to apply a pressure to brake the wheels of the aircraft, whereinthe pressure applied by each of the brake packs depends on theadjustment factor for the brake pack, and the pressure applied by atleast one of the brake-packs differs from the pressure applied byanother one of the brake-packs, and after outputting the control signal,receiving by the controller and while operating in the first and secondmodes, a second group of the input values each corresponding to arespective one of the brake packs, wherein a scatter value for thesecond group of the input valves is less than the scatter value for thefirst group of the input valves.